This research developed a new measurement technology for thermal analysis of the heat radiation from a hybrid transaxle case surface to the air and improved the heat radiation performance. This heat flux measurement technology provides the method to measure heat flux without wiring of sensors. The method does not have effects of wiring on the temperature field and the flow field unlike the conventional methods. Therefore, multipoint measurement of heat flux on the case surface was enabled, and the distribution of heat flux was quantified. To measure heat flux, thermal resistances made of plastic plates were attached to the case surface and the infrared thermography was used for the temperature measurement. The preliminary examination was performed to confirm the accuracy of the thermal evaluation through heat flux measurement. The oil in the transaxle was heated and the amount of heat radiation from the case surface was measured. The input energy and heat radiation amount were compared. As a result, it was found that the measurement was accurate to be within about 13%. In addition, thermal analysis with conditions simulating an actual vehicle was performed. The surface temperature distribution and heat flux distribution were measured and results were obtained that reflected the effects of internal oil flow path layout and cooling air flow. Based on these results, locations with a large potential for improved heat radiation performance were identified and it became possible to effectively improve heat radiation performance by installing fins at those locations to enlarge the heat radiation surfaces.